Impact of yellow leaf disease in sugarcane and its successful disease management to sustain crop production.

Abstract

Yellow leaf disease (YLD) caused by Sugarcane yellow leaf virus (ScYLV), a Polerovirus, Luteoviridae occurs in major sugarcane growing countries across the world. During late 1990s it was recorded in India. Although the disease was initially thought to be a minor disease in the country, by 2005 onwards the disease severity attained epidemic status across the states. Currently, the ruling varieties such as Co 86032, Co 0238, CoV 09356 etc in India are affected disease epidemics thereby cane productivity is reduced up to 50% and juice yield by 40-50% in severe cases. ScYLV and other sugarcane viruses causing and bacterium causing ratoon stunting disease, cause varietal degeneration in the field. Systemic accumulation of the viruses and the bacterium in high titre reduces vigour of the varieties in the subsequent vegetative generations or ratoons, hence their potential yield of the varieties could not be harnessed. Virus spreads to the field through infected setts and Melanaphis sacchari, sugarcane aphid is the insect vector which transmits the virus among the plants in the field. The virus was characterized on complete genome basis and about 10 genotypes were recognized across the countries. The genotype ScYLV-IND predominantly prevails in India. Various diagnostics, based on serological and molecular were developed for the virus, among them tissue blot and RT-PCR assays are commonly used. Among the disease management strategies, disease resistance and clean seed have the practical feasibility. Hence parental clones and pre-release varieties are screened for disease resistance in India. Virus elimination enabled through tissue (meristem) culture in combination with molecular diagnostics is the most efficient approach to contain the disease in the field and to address varietal degeneration. Such efforts led to varietal rejuvenation and increase in cane yield by 30-35% under field conditions.